cycling noise being caused by Broadband modem, help needed..

[pax-eterna]

I have noticed (with the new studio monitors -Eris 5's) that I am getting a cycling low pitched tapping - t.t.t.t.t.t.t.t.t.t.t that's about the best way I can describe it. it doesn't get louder when the spkr vol is turned up it stays pretty much the same and is relatively quiet, it's just there. Although it CAN be random. Sometimes it is there all the time and others, not a sound to be heard.

At first I thought it was the power supply as it went away when the modem pwr was disconnected. But it turns out it is the ethernet cables attached to the modem, particularly the one going to the PC (Intel NUC 8i7).

afaik, the ethernet cables to the modem are not shielded? And tbh, I wouldn't have a clue if they were or were not, soooo, question is would a shielded (if such a thing exists) ethernet (cat5?) cable help here?

Thanks

[Nazard]

Yes, you can buy shielded Cat5e cable, it's called Shielded Twisted Pair CAT5e, or, STP CAT5e.

You could also remove the cable between the NUC and modem/router and use wireless internet, if the modem/router has it and which the NUC supports. That might tell you whether the cable is the culprit.

The NUC is powered via a separate switched mode power supply and isn't grounded, so the issue may be a grounding one, called a 'ground loop'. This is the likeliest cause of the issue you describe.

[merlyn]

But it turns out it is the ethernet cables attached to the modem, particularly the one going to the PC (Intel NUC 8i7).

How did you determine that? I would guess you unplugged the network cable and the noise went away.

The noise may also go away if you unplug the connection between interface and monitors.

By talking about shielding you're imagining the interference is going through the air. It might be, but it probably isn't; it's more likely to be a loop of some sort, requiring both the network cable and the connection between the monitors and interface (computer).

Which connections are balanced, and which are unbalanced?

[Hugh Robjohns]

^ Yep.. my thoughts too. This is likely to be a ground-loop issue affecting the monitor speakers / interface.

[blinddrew]

Is the t.t.t.t.t. noise at a fixed frequency or does it vary at all?
Just wondering if there might be a clocking thing going on.

[pax-eterna]

Thanks folks, and apologies for late reply - I am in Oz so time differences apply...I am up now at 2.50am to try and respond in a more appropo time for you.
@blinddrew fixed frequency

@merlyn yes exactly, I simply unplugged and re-plugged, and all connections are balanced.

@Trevor Johnson - yes it is a separate PS, however I did not have this issue with former monitors? I think that might be the answer (re running wireless) .

Can this grounding loop (and I am happy to go with the consensus ) be random? I did notice yesterday afternoon, after all the "faffing" around, that the noise simply vanished. Only to re-appear this morning...but I will try the wireless and see what happens.

Thanks again for your (collective) time guys (gals?) appreciate it!

[merlyn]

@merlyn yes exactly, I simply unplugged and re-plugged, and all connections are balanced.

I see. That's slightly annoying, because balanced connections are meant to solve these sorts of problems.

This is then the floating earth problem because the PC is plugged into a DC power supply. I don't completely get that, but my own model of what's happening is that the NUC and the modem don't agree where earth (0V) is.

If it was me I would try an isolating transformer, where I would suggest an Orchid Electronics one if you were in the UK, but since you're in Oz -- an ART clean box or similar.

... but I will try the wireless and see what happens.

More of a workaround than a solution, but sure, it's likely to work.

[pax-eterna]

thanks Merlyn - I'll check out isolating transformers!

EDIT: haha, very expensive devices! I might just stick with WI-FI - that costs me nothing!

[merlyn]

I don't think they're hugely expensive :

https://www.storedj.com.au/art-pro-audi ... eliminator

but using Wi-Fi is cheaper.

There is another solution to this which is earthing the interface -- I'll leave that to someone else to explain.

[blinddrew]

Have we established if there's no solid earth in the system?

[merlyn]

As far as I can make out :

Monitors -- plugged into the wall -- earthed
PC -- PSU -- not earthed
Modem -- PSU -- not earthed

Because the PC is running on a PSU, this seems like 'laptop-itis' to me. A ground loop without a ground is a bit too Zen for me.

[blinddrew]

But the monitors are Eris 5s, which are type 1 so should be providing an earth for the system?